1. Field of the Invention
This invention relates generally to an improved surfactant system to prepare water-in-oil emulsion copolymers of 2-acrylamido-2-methylpropane sulphonic acid (AMPS) and an anionic comonomer. More particularly, the present invention utilizes a dual emulsion polymerization stabilizer mixture of sorbitan monooleate and a linear ABA block copolymer of polyesterpolyethylene oxide-polyester to produce the emulsion copolymers.
2. Description of the Prior Art
The preparation of water-in-oil emulsion polymers and copolymers is well known in the art and generally entails dissolving the monomer(s) in an aqueous phase, homogenizing the aqueous phase with an oil phase containing one or more emulsion polymerization stabilizers, and polymerizing the monomer(s). It was discovered that when attempting to produce copolymers of AMPS and anionic comonomers neither a conventional sorbitan monooleate polymerization stabilizer nor a conventional linear ABA block copolymer as disclosed in U.S. Pat. No. 4,203,877 alone were adequate to obtain a smooth polymerization profile, little or no coagulum formation during the polymerization, and a product having good long term storage stability.
Accordingly, it is an object of the present invention to produce a copolymer emulsion of AMPS and an anionic comonomer in which the polymerization profile is smooth, less than about 1% coagulum is formed during the polymerization, and the final emulsion product remains stable and ungelled after at least two months storage.